The two primary association strategies currently employed are candidate gene studies and GWAS. Candidate gene studies are driven by theory and focus on a specific gene because it is believed to be involved in the underlying biology associated with the behavior/disorder. The primary drawback to the candidate gene approach is that it is limited by our knowledge of etiological processes, which is often very incomplete when it comes to psychiatric disorders and related behavioral outcomes. Candidate gene research fell out of favor with the advent of GWAS. The primary advantage of GWAS is that this approach is not limited by our knowledge of the underlying biology of behavioral disorders; that is, GWAS is an atheoretical approach and since the whole genome is assayed for effects, there is no selection bias. GWAS have the ability to find novel susceptibility genes that, in turn, can help advance our understanding of the etiology of the trait or disorder. Several different companies now offer GWAS “chips” that have a predefined set of genetic markers that cover genetic variation across the genome. Although the exact
